Continuity mistake: The photo Edna sends to Bart differs when he shows his parents. The angle is different from what it was previously, revealing part of a photo frame on the wall which wasn't there before, and the sheets/pillows on the bed are different, and her eyes are closed when they look at it, but when Bart looked at it, they were open. (00:09:05 - 00:18:25)
Other mistake: In the end credits where it says, "Special Guest Voice", Marcia Wallace's name is there. Mrs. Krabappel was originally supposed to be in the episode but wasn't because Jose Canseco disliked his original part. He was originally slated to wake up in bed with her and miss the game, but Canseco's then-wife, Esther Haddad, objected. (00:29:00)
Continuity mistake: When Burns first shows the team the nerve tonic, the "&" on the 'Brain & Nerve Tonic' label is facing backward, but as Burns pulls it away it faces forward. Then as he moves it around as he's talking, the "&" switches between facing forward and facing backward again. This happens all in the one shot.